input validation using loop

Question

A loop in my class is not returning the expected value. It should return true when the value entered in the method is equal to one of the values in the area. When I compile and run my main method: "Please enter the id number to be checked" I enter 2 "you entered a number for the id" "565" "456" "342" "234" "237" "192" "237" "109" "278" "num u entered 2 true" "The value you entered is false" "Press any key to continue . . ."

The "num u entered 2 true" line is useless, and was just used for testing. Since 2 is not equal to any of the elements equal in the array, im not sure why it would remain false.

Here is my class.

public class Account
{
  int[] aNum = {565, 456, 342, 234, 237, 192, 237, 109, 278};
  boolean flag = false;

  public boolean aChecker(int num)
  {
    for(int i = 0; i < aNum.length; i++)
    {
      if(num == aNum[i]);
      {
        System.out.println(aNum[i]);
        flag = true;
      }
    }

    System.out.println("num u entered " + num + " " + flag);
    return flag;
  }

}

Here is my main method.

import java.math.*;
import java.text.DecimalFormat;
import java.io.*;
import java.util.*;


public class labBookFiftyThree {
  public static void main(String[] args) {
    Scanner myInput = new Scanner(System.in);
    Account myAccounts = new Account();

    int id = -1;
    while (id < 0) {
      System.out.println("Please enter the id number to be checked");
      if (myInput.hasNextInt()) {
        System.out.println("you entered a number for the id");
        id = myInput.nextInt();
      } else if (myInput.hasNext()) {
        System.out.println("Please enter a proper value");
        myInput.next();
      } else {
        System.err.println("No more input");
        System.exit(1);
      }
    }

    System.out.println("The value you entered is " + myAccounts.aChecker(id));
  }
}

It looks like your System.out.println("The value you entered is "+myAccounts.aChecker(id)); call is outside the loop. — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Aug 18, 2014 at 19:25
I think boolean flag = false; is in the wrong scope, it should probably be inside the aChecker function, so it can be reseted to false on each call. — Volune
– Volune, Commented Aug 18, 2014 at 19:27
I just proposed a format edit. you'll clearly see the incorrect if statement ;) — Xinzz
– Xinzz, Commented Aug 18, 2014 at 19:30
Out of curiosity, why did you put the ; at the end of the if line? Was it just a typo (your finger slipped), or were you confused by somebody teaching you that all statements had to end with a ;? I'm really wondering because I've seen this mistake happen a lot and I'm wondering if there's a flaw in how this is being taught. — ajb
– ajb, Commented Aug 18, 2014 at 19:30
Im stupid, my finger slipped and i added a ;, thank you all. — Ro Siv
– Ro Siv, Commented Aug 19, 2014 at 23:41

ajb · Accepted Answer · 2014-08-18 19:28:08Z

1

if(num == aNum[i]);
{
    System.out.println(aNum[i]);

    flag = true;
}

is equivalent to

if(num == aNum[i])
    /* do nothing at all */;
{
    System.out.println(aNum[i]);

    flag = true;
}

Because of the extra semicolon after the if, the System.out.println and flag = true are not part of the if statement. Therefore they will be performed whether or not the if condition is true.

Delete the last semicolon from the if line.

answered Aug 18, 2014 at 19:28

ajb

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